1. Field of the Invention
The present invention relates to a printer generally called "line printer" such as a thermal line printer or a wire-dot printer, or the like, more particularly, to a method for enhancing a fine line in the longitudinal direction of the printer, i.e., in the direction perpendicular to the printing line, and a circuit therefor.
2. Description of the Prior Art
Today, apparatus generally called a "line printer" is extensively available. This apparatus typically incorporates linearly arraying printing elements such as thermal elements or wires for providing dot impact for executing printing operation by making a printing medium (i.e., printing paper) able to drive itself in a direction perpendicular to the arraying direction of the printing elements. These line printers process image data given as black/white dot data or stored in memory in the form of binary encoded signals "1" or "0". The line printer then supplies those binary encoded signals to respective printing elements before eventually printing the original image data using these printing elements which are set either in the printing-activated or the printing-inactive state.
However, the line printers of the type mentioned above still have a problem to be solved. For example, when applying a recording density of more than 12-dot/mm of high resolution, width of longitudinal line (in the direction perpendicular to the arraying direction of the printing elements) by one printing element becomes significantly finer than the later line (in the arraying direction of the printing elements). In particular, this symptom is quite significant when an image is printed on a transparent film like the one used for overhead projectors, for example.
Furthermore, in applying thermal elements, due to restrictive conditions caused by wiring circuits, any one of these line printers needs to have the design of the heating element in a long and slender configuration in the direction perpendicular to the arraying direction of the printing element. As a result, when operating a thermal printer using thermal elements, fine lines in the longitudinal direction become extremely fine, thus causing poor visibility.
To solve these problems mentioned above, the inventors of this invention searched prior arts, so that Japanese Patent Laid-Open No. 56-40570 (1981) and another Japanese Patent Laid-Open No. 57-2775 (1982) for example were found. However, both of these prior art references merely make up identical picture elements with a plurality of thermal elements for making respective picture elements of a thermal printer to totally express themselves for printing identical picture elements with a plurality of thermal elements. As a result, the inventors could not confirm concrete means for fully solving those problems mentioned above.